In the conventional preparation of semiconductors a predetermined amount of extremely pure metal phosphide or arsenide is laid down on a substrate crystal. The conventional method of carrying out this process is to charge predetermined amounts of phosphine or arsine into a stream of hydrogen together with the appropriate amount of an organometallic compound. The mixed gas stream is passed through a furnace, at a predetermined temperature, which contains the crystal on which deposition is desired. At the predetermined temperature, an elimination reaction takes place whereby the organic portion of the organometallic is eliminated and replaced by phosphorus or arsenic as is appropriate. In order for this reaction to take place properly and efficiently the organometallic utilized must be sufficiently stable under the furnace conditions that it does not decompose per se and yet it must be sufficiently reactive to permit the elimination reaction to occur substantially instantaneously when the gas stream enters the heated furnace area.
Heretofore, the organic group used in the synthesis of the organometallic compounds has been the methyl group. However, the metalomethyls of this group are extremely volatile and pyrophoric, i.e., should the organometallic accidentally come into contact with air due to process errors, it would spontaneously inflame. This handling disadvantage makes it desirable to utilize alternative compounds.
The ethyl, isopropyl and isobutyl derivatives decompose too readily at elevated temperatures to permit the elimination reaction to take place in the proper manner.
In addition, a significant disadvantage of preparing semiconductors from phosphine and arsine is that these compounds are toxic and are stored as high pressure gases.
It has also been disclosed that organometallic molecules having .sigma. bonding between the Group III and Group V elements are effective precursors for the preparation of III/V compound semiconductor materials (A. H. Cowley, B. L Benac et al., "Organometallic Chemical Vapor Deposition of III/V Compound Semiconductors with Novel Organometallic Precursors", J. Am. Chem. Soc., 110, 6248-6249, 1988). These precursors have been found to be stable toward air and moisture, and are also sufficiently volatile for use in the gas phase synthesis of semiconductor materials. However, these precursors are made via a metathesis reaction or at high temperatures. In addition, lithium, sodium and potassium derivatives of Group V compounds and halogen derivatives of Group III compounds are used to make the precursors which add impurities to the final product.
Therefore, there still exists a need for a cleaner method which can take place at lower temperatures to minimize the amount of impurities.